The present invention relates generally to a shock absorption mount for use in supporting and protecting equipment, such as sensitive electronic equipment installed on an aircraft, a ship, or a submarine.
Traditionally, the U.S. Government and other governments have required that electronic equipment and other sensitive equipment used aboard military vessels, such as aircraft, ships, and submarines, be specifically designed and manufactured so as to withstand these vessels"" challenging operational environments. Accordingly, suppliers have had to specially xe2x80x9cruggedizexe2x80x9d or xe2x80x9cmilitarizexe2x80x9d equipment in order to satisfy certain testing criteria, such a shock testing and/or vibration testing.
Unfortunately, such militarized equipment has two significant drawbacks. First, specially designing each piece of equipment to withstand challenging operational environments can impose significant costs. Second, because each piece of equipment must be specially designed to meet testing criteria, the deployment of state-of-the-art technologies can be significantly delayed. For instance, an improved flat screen display technology may be readily available for commercial applications, but it may be years before the technology can be incorporated into military equipment.
As a result of these and other drawbacks of so-called xe2x80x9cMIL-SPECxe2x80x9d equipment, since the early 1990""s the Department of Defense has issued various directives permitting and, in fact, encouraging, utilization of so-called xe2x80x9ccommercial-off-the-shelfxe2x80x9d (COTS) technology. As a result, military vessels have been increasingly using COTS electronic components and systems in lieu of militarized equipment. COTS equipment is cheaper, it offers the latest technology, and in many instances, it offers a larger pool of suppliers from which the Government (or its prime contractors) can select.
One challenge presented by COTS equipment relates to its ability to pass shock and vibration requirements. Militarized equipment has traditionally been rigidly mounted to shipboard structures. However, COTS equipment tends to have limited capabilities to withstand shock and vibration motions, and, therefore, tends to be unsuitable for being rigidly mounted to shipboard structures. Therefore, COTS equipment usually requires isolation devices (shock mounts) to mitigate the effects of shock and vibration presented in the operational environment.
Typically, COTS equipment is placed in component racks that are coupled to a vessel structure (e.g., floor or wall) via one or more shock absorption mounts. Sometimes, individual pieces of equipment are coupled to the vessel structure via shock absorption mounts. Sometimes, COTS equipment is placed on flat platforms that, in turn, are coupled to the vessel structure, using shock absorption mounts.
Prior to deployment, equipment proposed for military vessel use is subjected to a standard series of tests. For example, the equipment may be subjected to an underwater explosive shock test (e.g., performed in accordance with MIL-S-901D) that can result in the transmission of more than one-hundred G""s of mechanical acceleration. The equipment may also be subjected to a vibration test (e.g., performed in accordance with MIL-STD-167-1) that may subject the equipment to as much as 1.25 G""s of acceleration and frequencies as, high as 50 Hertz.
COTS equipment affixed to some shock absorption mounts of the prior art, such as wire cable mounts, has failed shock testing due to insufficient mechanical damping as well as a lack of available deflection capability. Some shock absorption mounts of the prior art are also heavy and difficult to install. In addition, equipment affixed to some shock mounts of the prior art has failed vibration testing.
It is postulated that prior art shock mounts may have failed vibration testing for several reasons. First, a shock mount disposed between and affixed to a base structure and a piece of equipment forms an oscillator that is subject to resonant amplification of the base structure vibratory motion at the resonant frequency of the oscillator. Some shock mounts of the prior art have insufficient damping to maintain this resonant amplification at acceptable levels.
Second, some mounts of the prior art have a significantly high characteristic ratio of. vibratory resonant frequency to shock resonant frequency. Some mounts of the prior art exhibit a ratio of vibratory to shock resonant frequency of 1.4 or greater and thus exhibit excessively high vibratory resonant frequencies. Because the vibratory acceleration level at resonance is directly proportional to the square of the vibratory frequency, an increase in the vibratory resonant frequency of just a few Hertz can greatly increase the acceleration transmitted at resonance.
In sum, there is an increasing need for high performance shock mounts for the protection of sensitive equipment. While this discussion has focused on the needs of the military in this regard, it can readily be appreciated that a high performance shock mount may find application in other contexts, such as in nuclear power facilities or other facilities using sensitive electronic equipment.
An embodiment of the present invention comprises a generally C-shaped shock absorption mount that has a top section, a bottom section, and a supporting section. The top. section contacts an equipment mounting surface, while the bottom section contacts a foundation. The supporting section includes an inclining section, an intermediate middle section, and a declining section. The intermediate middle section has a curvilinear shape that has an elliptical inner segment and a circular outer segment.
According to one aspect of the invention, the inclining section is made up of a first substantially straight section and a second substantially straight section. The first substantially straight section defines an angle with respect to the ground plane defined by the bottom section. The second substantially straight section is approximately parallel to the ground plane. The declining section is made up of a third substantially straight section and a fourth substantially straight section. The third substantially straight section defines the same angle as the first substantially straight section, and the fourth substantially straight section is also approximately parallel to the ground plane.
According to another aspect of the invention, the shock absorption mount is constructed of an elastomeric material (or xe2x80x9celastomericxe2x80x9d having a flexural modulus in the range of about 10 to 100 ksi, a breaking strain greater than about 400%, and a yield strain greater than about 10% Preferably, the elastomeric is damped using a damping agent.
Accordingly, it is one object of the present invention to overcome one or more of the aforementioned and other limitations of existing systems and methods for providing shock and vibration isolation for COTS equipment.
It is another object of the invention to provide a shock absorption mount that attenuates shock excitations to acceptable levels.
It is another object of the invention to provide a shock absorption mount that attenuates vibration excitations to acceptable levels.
It is another object of the invention to provide a shock absorption mount that has a vibratory resonant frequency that is not significantly above the shock resonant frequency.
The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute part of this specification, illustrate several embodiments of the invention and, together with the description, serve to explain the principles of the invention. It will become apparent from the drawings and detailed description that other objects, advantages and benefits of the invention also exist.